U.S.-backed Syrian forces are reported to have advanced closer to an Islamic State stronghold on the border with Turkey.

The Syrian Observatory for Human Rights on June 18 reported the rebels had captured three villages from government control -- Zeitan, Khalsa, and Barna. The U.K.-based group said government forces and their allies had suffered serious losses.

The villages lie in a strategic area near a main highway that links Aleppo with the capital, Damascus.

The reported rebel advances came as Russian Defense Minister Sergei Shoigu held talks in Damascus with President Bashar al-Assad.

Shoigu also visited a Russian air base in the coastal province of Latakia.

Russia's military intervention in Syria in September helped Assad's government halt months of gains in western Syria by rebel fighters.

Russia, which has been bombing opposition-held areas, is blamed by the opposition and rights activists for causing hundreds of civilian deaths and targeting hospitals, schools, and infrastructure in what they say are indiscriminate attacks.